Alternator woes - only charging between 2400 and 2800 rpm? - Defender Source
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  #1  
Old June 11th, 2013, 10:21 AM
MonLand
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Loic Fabro
95 D90 - 96 Disco -06 LR3
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Alternator woes - only charging between 2400 and 2800 rpm?

I looked for similar symptoms but could not find matching threads, so I started a new one hoping someone would be able to chime in and help out.

Background information (maybe TMI, but I figured any detail might help?):
- D90 has what I believe is the stock alternator. About 80K miles on it (i.e. "brand new"! )
- Decided to play stupid and splash the crowd (which had already left....) on the last obstacle and went through a long puddle of (muddy/sandy) water.
- engine stalled after the puddle when back to idle
- after some convincing, engine restarted and could be kept running on 4, 5, 6 (???) cylinder when above 1200 rpm (or so?)
- engine dried up before getting back to camp
- stopped the truck, packed up, etc
- left camp site, drove a few miles and stopped at gas station.
- filled up
- when leaving gas station, I realized that the battery light was on and no rpm shown. Crap....
- Step 1: let wifey know that we are on our way home.
- Step 2: let wifey know that she might have to drive toward us instead of just waiting for you to at least entertain the 2x 6-year-old in the back while she helps recharging battery (or until tow truck arrives?).
- Step 3: google "how long can I drive without alternator" and keep looking until I find the answer I'm looking for ("2 hours" or "70 miles"). Of course the answer is "it depends on your battery and engine"... I was hoping to find some kind of formula or ballpark. [still interested if anyone has a number to share! ]
- Step 4: start praying that the alternator dries up (because it's not working only because it got wet, right?)

Anyway, while driving, I realized that the rpm came back between 2400 and 2800 rpm. Would register 0 below 2400 rpm or above 2800 rpm. This was reproducible at will.... This gave me more confidence that I'd make it home!

So, after helping a little more than usual to heat up the planet, got home, parked the truck away from everything knowing an alternator was in the cards and it'd take me a while to get to it.
Unfortunately, next day I had to move it.... And realized that the rpm were showing up across the range..... So much was hoping to troubleshoot this at a later time....

Anyway, I have not checked anything further than reading the gauges at the moment. But before I pull my voltmeter and check if the alternator puts out enough juice "now", I'd love to hear if anyone has seen the "alternator only works at a specific rpm range" before. I think I'll play safe and locate a spare alternator I'll leave in the truck so I'm not stranded when it dies (at some point it will die, right? ).

Thanks,
Loic.
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  #2  
Old June 11th, 2013, 10:52 AM
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o2batsea
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Bill Adams
66 109 sw 94 lwb
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Alternator charges at all RPM. The voltage regulator will allow current to flow to the battery when it senses that the voltage is below a certain set point, generally around 13-something volts.
My suspicion now that some time has passed and the internals of the alternator have dried out, is that it was simply soaked and was not charging properly.
Had a similar incident with a nearly new big screen Sony TV. Wife had a potted plant set on top of it. Watering day came around and, you guessed it, water went inside the TV chassis causing the TV to conk out with sparks, smoke and all kinds of consternation. Well it dried out overnight and was just fine the next day. It is still in service at my BIL's house.
I wouldn't worry if it is back to normal now.
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  #3  
Old June 11th, 2013, 11:36 AM
MonLand
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Loic Fabro
95 D90 - 96 Disco -06 LR3
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Anything I can do to waterize it a little better?
Like.... around the coil, on the distributor cap and wire plugs/boots, I'll put some dielectric grease to (try to) avoid losing cylinders next time. Should I just spray liberally WD-40 on the Alternator (once I confirmed it is not a conductor that is). I remember Charles offering to spray WD-40 last time we drove up the river at MAR to get some cylinders back (I just waited for them to dry up).
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Quote:
I have an ex MoD and an ex wife. The two no longer conflict with each other.
Quote:
it is not hoarding it is selective collecting
---
MonLand
1995 D90 NAS
1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )
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